The present invention relates to a light-sensitive polycondensation product comprising an aromatic diazonium salt and an aldehyde. The invention also relates to a light-sensitive recording material having a light-sensitive layer containing said polycondensation product.
It is known to produce polycondensation products by reacting aromatic diazonium salts, particularly diphenylamine-4-diazonium salts, with active carbonyl compounds, preferably formaldehyde. Condensation products of this type are described in U.S. Pat. No. 2,063,631. Their use in light-sensitive recording materials is described, e.g., in U.S. Pat. No. 3,235,383. Recording materials of this kind are widely used for industrial purposes, whereby products in which formaldehyde is used as the carbonyl compound for the condensation are practically the only ones which have gained acceptance. Other carbonyl compounds mentioned in the cited publications include higher aliphatic and aromatic aldehydes, ketones and quinones. A compound having differing carbonyl groups, namely anthraquinone-beta-aldehyde, is also mentioned. The reactivity of all these higher carbonyl compounds is lower than that of formaldehyde. This means that the reactions must be conducted under more severe conditions, e.g. more highly concentrated acids or higher temperatures must be used, which, in turn, favor the formation of by-products. In particular highly cross-linked, insoluble condensation products easily result from severe reaction conditions.
Although formaldehyde condensation products are still produced and used on a large industrial scale, they have the disadvantage that their composition and properties can only be varied to a very limited extent.
In more recent times it has been suggested to vary composition and properties by producing mixed condensation products, in the production of which a further second component which is condensible with formaldehyde is employed, in addition to a carbonyl compound and a diazonium salt. These products and their uses are described in U.S. Pat. No. 3,867,147. They can also be produced by condensing the diazonium salt with a second component which has been modified by introducing reactive groups. In the simplest case, the reactive groups are obtained by reacting formaldehyde with the second component. These condensation products yield high quality light-sensitive materials, in particular printing plates. Their production is more complicated, however, than the production of the simple formaldehyde condensation products, since it either requires a three component condensation reaction, which is more difficult to control, or a reaction in two stages.